1. Field
The present disclosure relates to an apparatus for the spatially resolved detection of objects located in a monitored zone having a transmission device for the transmission of electromagnetic radiation in a transmission region and having a reception device for the reception of radiation reflected from a reception region, with the transmission region and the transmission region overlapping or intersecting in a detection region which is disposed within the monitored zone, which covers a detection angle and in which the transmitted radiation is reflected by objects.
2. Background
Such detection apparatus are generally known, e.g. in the form of laser scanners which are formed as scanning laser distance measurement apparatus and which scan the detection region with a laser beam in a time pulsed or continuous manner. The distance measurement takes place in this respect e.g. in accordance with a time of flight (TOF) measurement principle or a phase measurement principle.
Such detection apparatus are mounted e.g. on vehicles to scan the vehicle environment and hereby to recognize objects such as other road users in the visual range of the apparatus. The vehicle is hereby so-to-say able to make a spatially resolved image and also—due to the possibility of measuring distances—a depth resolved image of its environment, with this environmental detection taking place in real time. A variety of applications are possible with the environmental data gained in this manner. Such detection apparatus are also used in industrial applications. It is in particular known for scanning TOF laser distance measurement units which should monitor a comparatively large angular range of up to 360° in at least one transmission or detection plane to deflect the scanning laser beam which is in principle one-dimensional, that is the transmitted radiation, within this plane with a preset angular resolution also determining the spatial resolution. It is known for this purpose to deflect the scanning beam—also called a measurement beam or travel beam—in the detection apparatus—also simply called sensors—by means of a motor-moved rotating prism or by means of a rotating mirror tilted e.g. by 45° to the optical axis. In these cases, the axis of rotation of the prism or of the mirror and the optical axis of the sensor extend parallel to one another. In an alternative aspect, the total electro-optical unit of the sensor can be set into rotation. In this respect, both the transmission aperture and the reception aperture are moved on a circular path to ensure that the scanning beam of the sensor sweeps over the desired angular range of up to 360°.
The aforesaid solutions have the disadvantage that comparatively large masses have to be moved, in particular set into rotation. The electrical power required for this purpose contributes to a not insubstantial degree to the total power consumption of the sensor. It is furthermore of disadvantage that the required storage of the rotating components significantly limits the service life of the sensor.
To eliminate these disadvantages, it has already been proposed to provide an imaging arrangement in the propagation path of the transmitted radiation and/or of the reflected radiation which covers the whole detection region at the transmission side and/or at the reception side at all times, with spatial resolution means additionally being provided which are formed to distinguish the reflected radiation with respect to the reflection site. For this purpose, reference is made to the not yet published European patent application of the applicant with the file reference EP 08 005 342 filed on Mar. 20, 2008. Although solutions are provided with this which work satisfactorily, there is still a need to improve the detection of objects. It is in particular difficult to impossible with the solutions described in the named application to scan the monitored zone at different vertical positions, i.e. the known solutions are so-to-say not capable of elevation with respect to a practical implementation capability. In practice, however, it is desirable to scan the monitored zone not only in a single plane, in particular a horizontal plane, in an angular range of up to 360°, but it is additionally desirable for a number of applications additionally to carry out the scanning at different vertical positions.
A further problem in connection with the known solutions is the fact that the sensitivity of such a detection apparatus, in particular of a laser scanner, is generally a function of the object distance as well as of the offset between the optical transmission system and the optical reception system. In a number of cases, the design of the detection apparatus has the effect that the optical transmission system and the optical reception system cannot be arranged so close to one another as would be desirable for a sensitivity of the detection apparatus satisfying specific demands. In particular an insufficient sensitivity or even “blindness” in the so-called near zone of the detection apparatus results from this since a sufficient overlap of the transmission region and of the reception region is only adopted at larger distances from the detection apparatus.